Configurable analog front-end for mutual capacitance sensing and self capacitance sensing

1. A dual mode capacitance sensing circuit, comprising:

a capacitance-to-voltage converter including an amplifier and an integration capacitance coupled between an output and an inverting input of the amplifier;

a first switching circuit responsive to mutual mode control signals for controlling supply of signals from a sense node of a capacitive touch matrix to the capacitance-to-voltage converter in a mutual capacitance sensing mode and responsive to self mode control signals for controlling supply of signals from a force node of the capacitive touch matrix to the capacitance-to-voltage converter in a self capacitance sensing mode, wherein the capacitance sensing circuit is configurable for operation in the mutual capacitance sensing mode or the self capacitance sensing mode;

a floating node with a first capacitance between the floating node and the sense node and a second capacitance coupled between the floating node and the force node; and

a second switching circuit configured to selectively apply high, common mode and low voltages to the floating node depending on operation in the mutual and self capacitance sensing modes.

2. A dual mode capacitance sensing circuit as defined in claim 1 , wherein the capacitance-to-voltage converter further comprises a switching element connected across the integration capacitance to perform reset in the mutual and self capacitance sensing modes.

3. A dual mode capacitance sensing circuit as defined in claim 1 , wherein the first switching circuit comprises a switching element connected in series with the inverting input of the amplifier and configured to connect sensing signals to the inverting input during portions of the mutual and self capacitance sensing modes.

4. A dual mode capacitance sensing circuit as defined in claim 1 , wherein the capacitance-to-voltage converter further comprises a switching element configured to connect the inverting input of the amplifier to the common mode voltage during at least a portion of the mutual capacitance sensing mode.

5. A dual mode capacitance sensing circuit as defined in claim 1 , wherein the capacitance-to-voltage converter has a single-ended input and a differential output.

6. A dual mode capacitance sensing circuit as defined in claim 1 , further comprising a third switching circuit including chopper switching elements configured to connect the force node to the high voltage in portions of the mutual capacitance sensing mode and in portions of the self capacitance sensing mode and to connect the force node to the low voltage in portions of the mutual capacitance sensing mode and in portions of the self capacitance sensing mode.

7. A dual mode capacitance sensing circuit as defined in claim 1 , wherein the second switching circuit comprises a switching element configured to connect the floating node to the low voltage in portions of the mutual capacitance sensing mode and in portions of the self capacitance sensing mode.

8. A dual mode capacitance sensing circuit as defined in claim 1 , further comprising a third switching circuit including chopper switching elements configured to alternately connect the sense node to the high voltage and to the low voltage in portions of the self capacitance sensing mode.

9. A capacitance sensing circuit of claim 1 , wherein the first and second capacitances are parasitic capacitances.

10. A capacitance sensing circuit operable in a mutual sensing mode or in a self sensing mode, comprising:

a capacitance-to-voltage converter comprising an amplifier and an integration capacitance coupled between an output and an inverting input of the amplifier;

first, second and third sense switching elements coupled between a sense node and an input voltage, a common mode voltage and ground, respectively;

first, second and third force switching elements coupled between a force node and the input voltage, the common mode voltage and ground, respectively;

first, second and third floating switching elements coupled between a floating node and the input voltage, the common mode voltage and ground, respectively;

a sense node switching element coupled between the sense node and the inverting input of the amplifier; and

a force node input switching element coupled between the force node and the inverting input of the amplifier.

11. A capacitance sensing circuit for a capacitive sensing panel including a plurality of first lines intersecting a plurality of second lines, wherein a mutual capacitance exists between each pair of intersecting first and second lines, comprising:

a capacitance-to-voltage converter comprising an amplifier and an integration capacitance coupled between an output and an inverting input of the amplifier;

a first switching circuit configured to selectively connect the inverting input to one of said first lines or one of said second lines;

a second switching circuit configured to selectively connect an input voltage, a common mode voltage and a ground voltage to said one of said first lines depending on operation of the capacitive sensing panel in self capacitance mode and mutual capacitance mode; and

a third switching circuit configured to selectively connect the input voltage, the common mode voltage and the ground voltage to said one of said second lines depending on operation of the capacitive sensing panel in self capacitance mode and mutual capacitance mode.

12. The capacitance sensing circuit of claim 11 , further comprising:

a floating node;

a first capacitance between the floating node and said one of said first lines;

a second capacitance between the floating node and said one of said second lines; and

a fourth switching circuit configured to selectively connect the input voltage, the common mode voltage and the ground voltage to said floating node depending on operation of the capacitive sensing panel in self capacitance mode and mutual capacitance mode.

13. The capacitance sensing circuit of claim 12 , wherein the first and second capacitances are parasitic capacitances.

14. A capacitance sensing circuit for operating a capacitive touch screen in both a mutual sensing mode and in a self sensing mode, comprising:

a capacitance-to-voltage converter comprising an amplifier and an integration capacitance coupled between an output and an inverting input of the amplifier;

a sense node switching element coupled between a sense node of the capacitive touch screen and the inverting input of the amplifier;

a force node input switching element coupled between a force node of the capacitive touch screen and the inverting input of the amplifier;

a first switching circuit configured to selectively apply an input voltage, a common mode voltage and a ground voltage to the force node depending on operation of the capacitive touch screen in mutual sensing and self sensing mode;

a second switching circuit configured to selectively apply the input voltage, the common mode voltage and the ground voltage to the sense node depending on operation of the capacitive touch screen in mutual sensing and self sensing mode; and

a third switching circuit configured to selectively apply the input voltage, the common mode voltage and the ground voltage to a floating node of the capacitive touch screen depending on operation of the capacitive touch screen in mutual sensing and self sensing mode.

15. The capacitance sensing circuit of claim 14 , further comprising:

a first parasitic capacitance between the floating node and said sense node; and

a second capacitance between the floating node and said force node.